"No, I've tried to think back those years and I'm trying to remember if there was anything significant like that but I can't recall anything," he said.

But Dr. Calne says his own research suggests there is a higher incidence of Parkinson's among people who are frequently exposed to viruses.

"It's common in teachers, the medical workers, and it's very uncommon in people who are at home all the time," he said.

To date, no one has established a link between Parkinson's Disease and viruses or other environmental causes. But there are some studies under way -- one at the University of Washington and another at the Mayo Clinic.

For now, Calne's theory remains just that -- an intriguing theory that, at the very least, raises some interesting questions.